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# Physics.....Calculate Terminal Velocity? Watch

1. Droplets in a deodorant spray have a mass of about 4*10^-12 kg
estimate the the terminal velocity in air of viscosity 2*10^-5
2. Direct yourself to the 'Maths, Science, and Technology Help' sub-forum in future when asking these sorts of questions. Anyway, I haven't done much about terminal velocity but maybe this website would help you? http://www.sciencebyjones.com/viscosity.htm

You just need to find the speed at which the force of gravity equals the forces acting upwards . . .
3. (Original post by reb0xx)
Droplets in a deodorant spray have a mass of about 4*10^-12 kg
estimate the the terminal velocity in air of viscosity 2*10^-5
There is one force acting downwards, the weight of the particle. That's just mg.

There are two forces acting upwards

*the viscous drag force F
*the buoyancy (Archimedes upthrust) force U

At terminal velocity mg = F + U

The F term for viscous drag includes the velocity which you are trying to calculate.

Do you have formulas for F and U?

Note: some questions will direct you to ignore the U term.
4. (Original post by Stonebridge)
There is one force acting downwards, the weight of the particle. That's just mg.

There are two forces acting upwards

*the viscous drag force F
*the buoyancy (Archimedes upthrust) force U

At terminal velocity mg = F + U

The F term for viscous drag includes the velocity which you are trying to calculate.

Do you have formulas for F and U?
F=6pirnv always.
5. (Original post by Mr Edexcel)
F=6pirnv always.
Put that equal to mg and calculate v.
You have m, r and n (viscosity) all given. Assume values for g and Pi.
If you are supposed to include the U term you need to know the density of air. Is it given?

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